A particularly well-rounded set of thoughts on keywording in Lightroom from Chuq Von Rospach here:
An important point — when you design a structure like this, how well it’ll work for you depends on where your hassle factor hits. Are you more annoyed by looking through long lists of things? If so, design a hierarchy with more sub items and fewer items in each sub-area. If traversing the tree bothers you more, use longer lists and fewer sub-items. You can adjust this to your tastes as you work with it.
Define some standards and then stick to them. Capitalization, tense, punctuation and the like matters. If you aren’t consistent here, your work will come across as unprofessional and sloppy — even if people looking at your photos only notice it sub-consciously. In my keywords, I standardized on using the plural form (“Birds” instead of “Bird”) unless that was clearly inappropriate, and I lean towards a third person form, present tense and I always strive to use an active voice instead of passive. (Passive Voice writing is to be hated in all serious writing).
Getting all of the details right is — frankly — a pain. But once you get them right, they’ll stay that way with minimal work, and it gives a polish and professionalism to your work that leaves a better impression.
It’s worth reading Chuq’s thoughts in full because they are well-written and include some “theoretical” angles while not forgetting the practical, real world issues. The first paragraph I’ve quoted rings particularly true here – it’s why I use one long list.